On loan from the Archdiocese of Arlington, Virginia, Reverend Riley, a Guinness drinker, opened with a prayer as the people in the packed bar bowed their heads. The crowd, mostly in their twenties and early thirties, and presumably Catholic, had gathered to listen to Riley address the night's topic "Confessions From the Other Side of the Screen." In the middle of the Lenten season, it was an appropriate topic.

Confession, Riley explained, is commonly misunderstood. "A lot of people think of confession as an ecclesiastical slap on the wrist," he said. "You are in trouble, so you are going to get punished."

He joked that he used to think wearing his clerical collar was a guarantee to heaven -- but he knows know that everyone, even a priest, sins and must repent.

"A lot of people think that Lent is more about giving up meat on Fridays but it is really a season of repentance and mercy," he said. "As Catholics, the most important place where we celebrate the beautiful mercy of God is in the sacrament of confession.

A professor at the Augustine Institute, Riley is no stranger to Theology on Tap. He has spoken at gatherings in Arlington and Cincinnati, discussing topics ranging from the history of the life of Christ to scripture and the Holy Eucharist.

Started in Chicago in 1981, TOT meetings are now held in more than thirty cities across the country; Denver bars have been hosting TOT sessions for more than a decade, serving as a social space where young adults can learn more about their faith and the Catholic community. In Denver, discussions have covered everything from porn, contraception and homosexuality to responsible citizenship and human trafficking.

The crowd at Katie Mullen's listens to Rev. John Riley speak.

Initially TOT met only six to eight times a year here, but demand has made it a monthly event, according to Kate Sweeney, a TOT volunteer. Sweeney, who is also involved in Denver Catholic Young Adults, says that social media, including TOT's Facebook page and youth initiative, are making an impact locally.

"We are the church," Sweeney said of the Catholic youth movement in Denver. "That is what is so cool about Theology on Tap. We are living our faith in the place we are, not just in church on Sunday."

But TOT has not been immune to push-back. The bar where it was meeting last year asked the group to find a new location after some discussion topics proved too controversial. Approached by the archdiocese, Katie Mullen's was happy to host. "We have a close relationship with the Holy Ghost and the parish here. The Irish pub mentality is to be involved in the community and what is around them," explained David Caughey, Katie Mullen's general manager.

TOT is a good group with good energy, he added. Plus the meeting fills half the bar, even on the Monday after St. Patrick's Day.

"I was really stunned by the number of people here," said Allison Zucco, who was attending for the first time. A friend had invited Zucco, a 25-year-old physical therapy graduate student at Regis University; she plans to come again.

"I come for the social atmosphere, the talks. And it's nice to be around a Catholic community in public," said Mike Rogers, a 28-year-old engineer from Centennial. he's been attending for more than a year; he heard about TOT through a friend and is also involved in the Catholic Young Adults sports league.

While TOT is a Catholic event, anyone of any faith is welcome to attend. "If we are going to be effective heralds of the new evangelization, we can't just sit in church and wait for people to come to us, we've got to go to them," said Reverend Riley. "And as an Irish Catholic, I think Katie Mullen's is the best place start."

After his talk, he told the crowd he would accept any drinks they would like to buy for him when he returned from Holy Ghost Catholic Church, where he was hearing confessions that night.